crypto: sm2 - fix a memory leak in sm2

SM2 module alloc ec->Q in sm2_set_pub_key(), when doing alg test in
test_akcipher_one(), it will set public key for every test vector,
and don't free ec->Q. This will cause a memory leak.

This patch alloc ec->Q in sm2_ec_ctx_init().

Fixes: ea7ecb66

 ("crypto: sm2 - introduce OSCCA SM2 asymmetric cipher algorithm")
Signed-off-by: Hongbo Li <herberthbli@tencent.com>
Reviewed-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>